• Journal of Korea Multimedia Society
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• v.9 no.9
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• pp.1131-1138
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• 2006

This paper proposes a novel method for grading of underground communication conduits by laser projection image analysis. The equipment thrust into conduit consists of a laser diode, a light emitting diode and a camera, the laser diode is utilized for generating projection image onto pipe wall, the light emitting diode for lighting environment and the image of conduit is acquired by the camera. In order to segment profile region, we used a novel color difference model and multiple thresholds method. The shape of profile ring is represented as a minimum diameter and the Fourier descriptor, and then the pipe status is graded by the rule-based method. Both local and global features of the segmented ring shaped, the minimum diameter and the Fourier descriptor, are utilized, therefore injured and distorted pipes can be correctly graded. From the experimental results, the classification is measured with accuracy such that false alarms are less than 2% under the various conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.5
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• pp.399-406
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• 2016

The large scale wind turbine blades usually experience periodic change of inflow speed due to blade rotation inside the ground shear flow region. Because of the vertical wind shear, the inflow velocity in the boundary layer region is maximum at uppermost position and minimum at lowermost position. These spatial distribution of wind speeds can lead to the periodic oscillation of the 6-component loads at hub and low speed shaft of the wind turbine rotor. In this study we compare the aerodynamic loads between two inflow conditions, i.e, uniform flow (no vertical wind shear effect) and normal wind profile. From the computed results all of the relative errors for oscillating amplitudes increased due to the ground shear flow effect. Especially bending moment and thrust at hub, and bending moments at LSS increased enormously. It turns out that the aerodynamic analysis including the ground shear flow effect must be considered for fatigue analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.10
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• pp.1269-1278
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• 2013

The cutting area changes periodically in the end-milling process because of its form generation mechanism. In this study, the effects of the cutting area on end-milled side walls are studied by developing a cutting area model that simulates the area formed by engagement between a workpiece and a cutting edge of the end mill. To do this, the straightness profile of the side wall in the axial direction is investigated. Models for estimating the cutting area and the transition point, where the slope of the straightness profile changes suddenly, are verified from real end-milling experiments under various radial and axial depth of cut conditions. Through this study, it is confirmed that the final end-milled side wall is generated in the regions where cutting areas are constant and decreasing in the down-cut. Similarly, in stable up-cut, it is also generated in the regions where cutting areas are increasing and constant. It is found that the transition point appears when the region changes.

• Aerospace Engineering and Technology
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• v.4 no.2
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• pp.27-35
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• 2005

In this study, a performance analysis code was developed for the off-design performance analysis of air turbo ramjet(ATR) engine, and the analyses were performed for the pre-designed ATR engine at several operating points in the envelope. Variable intake and thrust nozzle were assumed to cover the wide envelope. Mathematical models for each components were developed to calculate their off-design performance. Simple design formulas were introduced for some components to explore the performance variation versus the design parameters. As a result, the pre-defined engine couldn't cover the entire mission profile. And it was also found that the effect of the pre-cooler was not very great, especially in the region of low Mach number.

• Aerospace Engineering and Technology
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• v.7 no.2
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• pp.110-116
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• 2008

This paper gives a brief summary of the TVC battery design description, specifications and test results. The TVC battery for KSLV-I upper stage contains 168 Sony l8650VT high power lithium-ion cells. It configured as 2 strings in parallel, with each string containing 84 series connected cells. This allows to meet nominal 270V voltage and capacity requirements specified for the mission of the Thrust Vector Control(TVC) system. The loads profile of the TVC system has short duration, high current pulse. To power such a system with minimal mass, the battery employed l8650VT Cells. This cell is specifically designed for high rate applications and is capable of a 10C continuous discharge.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.25.3-26
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• 2008

The direct way to the moon is to start from the parking orbit by using impulsive thruster In previous domestic research, the direct way has been studied by using a single impulsive shot. However, when a single impulsive shot occurs to go into a Translunar orbit, gravity losses occur because thruster is not impulsive shot but the finite burns and it causes the gravity losses. To make up for the weak point of a single impulsive shot, this paper divides TLI (Trans Lunar Injection) into several small burns. Therefore, departure loop trajectory and the Translunar trajectory. This method is useful not only to reduce the gravity losses but also to check the condition of satellite. By using this method, this paper demostrates the optimized trajectory from Earth parking orbit to lunar mission orbit which minimizes the fuel, and the SNOPT (Sparse Nonlinear OPTimizer software) is used to find optimal solution. Also, this paper provides lunar mission profile which includes the mission schedule when TLI, LOI (Lunar Orbit Insertion) maneuvers occur, a mount of fuel when thruster is used and other mission parameters.

• Journal of Pharmaceutical Investigation
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• v.32 no.4
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• pp.327-330
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• 2002

Alginate based polymeric matrices were designed for controlled release and stabilization of cefaclor in gastrointestinal fluid. Cefaclor is known to be acid stable and subjected to be degraded at neutral and alkaline pHs. In order to achieve an effective release profile of cefaclor in gastrointestinal tract, a particular strategy in dosage form design should be required from the view point of maintaining its activity. The amphiphilic nature of cefaclor allowed its controlled release using ionic polymers based on ionic interaction between the drug and polymers. The thrust of this study was to develop a technique that delivers cefaclor keeping effective release rate in the intestinal tract. Considering the fast degradation of cefaclor in the intestinal fluid, the matrices were designed to release surplus amount of cefaclor. The alginate based matrices demonstrated increase in release rate in the simulated intestinal fluid, which was favorable to compensate the degraded portion of cefaclor. In addition, stabilization of cefaclor in the intestinal fluid was obtained by employing citric acid that provides an local acidic environment. The matrices might be valuably used for the development of an oral cefaclor dosage form.

• Journal of Astronomy and Space Sciences
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• v.11 no.2
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• pp.296-307
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• 1994

Using X-Window system (Motif Graphic User Interface), the AKM (Apogee Kick Motor) firing software for Koreasat which will be launched in 1995 has been developed to transfer the spacecraft from its transfer orbit, provided by the DeltaII launch vehicle, into a nearly geostationary drift orbit. The AKM firing software runs in one of two modes. In mission analysis mode, using a fixed magnitude impulsive velocity change, it provides the necessary data for planning the burn parameters. In insert mode, it uses the orbit propagator function to integrate the spacecraft state through the AKM burn. In this case, an AKM thrust profile and specific impulse are applied to the necessary data for planning the burn parameters to obtain the best possible drift orbit. The apogee burn planning simulation for orbital transfer of Koreasat has been performed using the AKM firing software. And the result of this simulation has been analyzed.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.5
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• pp.35-47
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• 2011

Dynamic characteristics of a flow control valve, which plays an important role in thrust and O/F control of liquid rocket engines, have been analyzed by the AMESim simulator modeling. The speed control method was proposed for the control of the flow valve equipped with a BLDC motor. The experimental results demonstrated the feasibility of systematical application as well as the performance of the speed control method. Moreover, the speed control method for BLDC motor is much simpler than the P control method in complex flow systems. With the speed control method, the control flow characteristics were evaluated according to plunger shapes. Consequently, same plunger shape proved to be more efficient in the mixture ratio control operated by two flow valves. It was also shown that the appropriate modification of plunger shapes could reduce the mixture ratio perturbation by 0.5%.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.7
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• pp.652-659
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• 2011

A computational system to predict flowfield and infrared signature in aircraft exhaust system is developed. As the first step, a virtual mission profile is considered and an engine is selected through a performance analysis. Then a nozzle that meets the requirement of each mission is designed. The internal flow in the exhaustion nozzle at the maximum thrust is analyzed using a state-of-the-art CFD code. In addition, a system to combine information of the skin temperature distribution of the nozzle and after-body surface with an infrared prediction code is developed. Finally, qualitative results for the infrared signature reduction design are obtained by investigating the infrared signature level under various conditions.